We are studying small intestinal transport and its regulation. Stimuli that enhance and suppress total intestinal absorption and specific absorption per unit of mucosa are being examined. Stumuli include diabetes, intestinal resection, alterations in composition of diet, and dietary restriction. Substrates under investigation include hexoses, amino acids, peptides, sodium, calcium and magnesium. Absorption is measured in vivo by luminal perfusion of the entire small intestine for determining total intestinal absorption. Individual intestinal sites are perfused to determine the locus of maximal enhancement and suppression of absorption. Absorption kinetics are measured at the site of maximal adaptation. Intestinal function and its response to stimuli is correlated with crypt cell proliferation rate, mucosal cell transit time from crypt to villus tip, synthesis and degradation of protein by mucosal absorptive cells. Protein synthesis by mucosal cells is utilized to identify transport proteins. The mechanisms of intestinal calcium absorption and its regulation is examined at intestinal sites from duodenum to colon. The role of calcium binding protens and associated hormonal mechanisms are also being studied.